FR3097641A1 - METHOD OF MANUFACTURING A CHARACTERIZATION TEST - Google Patents

Abstract

Title: Process for manufacturing a characterization specimen. The invention relates to a method for manufacturing a characterization specimen (20) comprising successive direct depositions of metal from a plurality of mono-cords (21) on a substrate (22), characterized in that, after the deposition of each mono-bead, a delay is applied before the deposition of the following mono-bead, the delay period being defined so as to allow the cooling of the deposited mono-bead below a target temperature. Figure for abstract: Fig. 2

Description

Process for manufacturing a characterization specimen.

The present invention relates to the field of the repair of aeronautical parts, and more specifically to the manufacture of specimens making it possible to reproduce the microstructural and thermomechanical characteristics of a repaired aeronautical part.

One-piece bladed parts are increasingly used in aeronautical turbomachines because they allow very significant weight savings thanks to the disappearance of the blade root retaining system. However, when the blades of such a part are worn or damaged, they cannot be replaced. Due to the very high value of these components, in particular due to their compositions or the complexity of their production processes, it has become interesting to seek a solution to repair them, in particular for the most frequent case of damage. : regular wear of the tips of the blades by friction. Indeed, the reduction in the height of the blades caused by their use leads to a loss of tightness of the stages of the turbomachine and therefore a drop in its efficiency.

A repair process carried out by removing the damaged blade portion and then replacing it with a new element welded to the initial part has been proposed, for example, in application US2006/277753. However, it does not offer complete satisfaction because it is complex to implement and also requires treatment of the welds once they have been made.

In recent years, the emergence of additive manufacturing, in particular direct metal deposition (DMD) processes, has made it possible to consider new repair methods. It was for example envisaged in the document US2006/193612 to deposit by direct deposition of metal, at the top of a damaged blade, a surplus of material in order to restore the blade to its initial appearance. Direct metal deposition involves a very localized supply of energy and generates very pronounced thermal gradients in the components as well as very rapid cooling. These particular solidification conditions, sensitive to the parameters of direct metal deposition, are at the origin of a microstructure of the repaired zone different from that of the initial forged part. In particular, the end of the blade where the deposition took place must be studied very carefully in order to guarantee fatigue resistance once the part has been repaired.

To study the repaired part, non-destructive checks can be carried out after repair to identify possible defects, but no information on the final microstructure of the repaired part can be obtained, because obtaining information on the microstructure requires destructive controls, which do not, by definition, allow the part thus controlled to be used.

In addition, the thermal conditions encountered when direct metal deposition takes place are not easily reproducible during the manufacture of a characterization specimen. Indeed, the direct deposition of metal involves a very localized supply of energy and generates very pronounced thermal gradients in the components, or, in the case of a one-piece bladed part, the whole of the part plays during the deposition. a much greater role as a heat sink than that played by the body of a smaller characterization specimen. This thermal pumping causes different thermal conditions during direct metal deposition between the one-piece bladed part and a characterization specimen created by direct metal deposition under the same conditions, so that the latter does not faithfully reproduce the microstructure of the bladed part. monobloc, and is therefore not satisfactory for characterizing the thermomechanical behavior of the repaired monobloc bladed part.

There remains an industrial need for a process for manufacturing a characterization specimen that is representative of a bladed part repaired by direct metal deposition in order to be able to study its microstructure and thermomechanical properties.

The present invention aims precisely to meet this need.

The invention relates to a method for manufacturing a characterization specimen comprising direct metal deposition of a plurality of mono-cords on a substrate, characterized in that, after the deposition of each mono-cord, a delay before depositing the next single bead, the delay time being defined so as to allow the deposited single bead to cool below a target temperature.

This manufacturing process makes it possible to obtain a specimen that faithfully reproduces the characteristics of a bladed monobloc repaired by direct metal deposition, particularly in terms of microstructure.

In one embodiment, the target temperature can be defined as the temperature obtained at the surface of a blade of a bladed one-piece part after the deposition of a mono-bead during the repair thereof by direct deposition of metal. Such a choice of the target temperature makes it possible to ensure that the deposition of single beads in the manufacturing process of a characterization specimen takes place at a temperature equal to the temperature at which the deposition of single beads takes place during the repair of a bladed one-piece part. In other words, the delay time makes it possible to simulate the heat pumping of the real part by allowing the specimen to cool down to the temperature reached by a bladed one-piece part during the repair process, before deposition. of the next mono-cord.

In this embodiment, and by choosing identical conditions for the direct deposition of metal from the manufacturing process of the characterization specimen and those for the repair of a bladed one-piece part, the deposition of single beads from the manufacturing process of the characterization specimen takes place under conditions identical to those of the single-bead deposition for the repair of a bladed one-piece part.

In one embodiment, once the target temperature has been chosen, the time delay required for the surface of the specimen receiving the deposit of a mono-bead to be at a temperature equal to the target temperature can be determined by the numerical evaluation of an equation giving the temperature at any point of the specimen as a function of the time delay. Such a method allows the determination of the dwell time in a simple and inexpensive manner. In addition, it is easily adaptable to specimens of all kinds, since the equation giving the temperature at any point of the specimen as a function of the time delay depends only on the geometry of the specimen, the parameters of the materials of specimen and single bead as well as the characteristics of the laser used.

By delay, it is understood a process step during which no action is actively carried out on the characterization specimen during manufacture. In particular, the latter is not, throughout the duration of the time delay, subjected to any heating or direct deposit of metal.

For example, such a delay can be achieved by cutting off the power supply to the device used for direct metal deposition for a period equal to the delay duration. It is also possible, and possibly simultaneously with the shutdown of the energy supply to the device, to cut off the supply of material to the sample. For example, in the case of metal deposition by laser such an interruption can be made simply by shifting the nozzle bringing the powder out of the surface of the sample.

By direct metal deposition (or DMD for the English acronym "Direct Metal Deposition"), we mean an additive manufacturing process in which a deposition head comprises an energy beam (for example an electron beam or a laser) which encounters a metal wire or a stream of focused metal powder to melt the metal, and deposit the drops of molten metal to form a pool of molten metal on a surface. Cooling the bath gradually forms a layer. The laying head can move to form layer by layer the part portion to be manufactured. The direct metal deposition process is also known by the English term "Direct Energy Deposition" (DED).

For example, direct metal deposition can be laser metal deposition (LMD for the English acronym “Laser Metal Deposition”), electron beam metal deposition (EBMD for the English acronym “Electron Beam Metal Deposition”) or an arc-wire additive manufacturing process (WAAM for the English acronym “Wire Arc Additive Manufacturing”).

Preferably, in a manufacturing method of the invention, the direct metal depositions are made by laser metal deposition (LMD).

The method of manufacturing a characterization specimen is not limited by the composition of the single beads deposited by direct metal deposition. The mono-beads of the process are chosen identical to those used for the repair of a bladed monobloc that we want to characterize.

For example, mono-cords can be made of titanium-based or nickel-based alloys, and in particular Ti-6Al-4V, inconel 625, inconel 718 or even hastelloy ® or Waspaloy ® .

Similarly, the manufacturing process is not limited by the nature of the substrate. The substrate is chosen to be identical to those of the bladed monobloc whose repair is to be characterised. For example, the substrate may be a titanium-based alloy, and in particular a Ti17 or Ti-6Al-4V alloy or a titanium-based alloy, in particular inconel 625, inconel 718 or even hastelloy ® or Waspaloy®.

In a manufacturing method, the mono-cords of the plurality of mono-cords can be arranged one above the other. Such an embodiment makes it possible to obtain characterization specimens for which the deposition of mono-beads is identical to that carried out most frequently to repair the blades of single-piece bladed parts by direct metal deposition.

The manufacturing process can also include steps other than the direct deposition of successive metals of a plurality of mono-cords. For example, the method may further comprise a final machining step to obtain a characterization specimen having a particular shape, for example a characterization specimen suitable for tensile tests.

In one embodiment, the substrate/deposit interface can be located in the useful zone of the characterization specimen. Such an embodiment makes it possible to precisely characterize this interface.

The useful zone of the test piece is defined as the zone of the test piece that it makes it possible to characterize.

According to another of its aspects, the invention also relates to the use of a characterization specimen manufactured by a method as described above.

In particular, such a use includes all the characterization methods that can be applied to the test piece and making it possible, for example, to characterize the microstructure of the test piece, in particular at the level of the junction between the substrate and the plurality of mono-cords, or still all the uses of the specimen to determine its thermomechanical properties.

Such use makes it possible to study the behavior of a bladed one-piece part repaired by direct metal deposition, in particular by carrying out destructive testing, since the characterization specimen obtained by the method described above has microstructural properties similar to those of a one-piece bladed part repaired by direct deposition of metal, while being obtained by a less expensive and faster process than a one-piece bladed part.

Figure 1 is a representation of a bladed one-piece part.

FIG. 2 schematically represents in a front view a specimen obtained in one embodiment.

FIG. 3 schematically represents in a transverse view a specimen obtained in the same embodiment as that of FIG. 2.

FIG. 4 schematically represents in a front view a plurality of characterization specimens obtained by the method of the invention, in another embodiment than that of FIGS. 2 and 3.

FIG. 5 represents a result obtained by numerical evaluation of an equation giving the temperature as a function of the delay time.

FIG. 1 represents a bladed one-piece part 10 whose mechanical behavior and microstructure is reproduced by a characterization specimen obtained by the method of the invention. The blades 11 of the part have a free end 12 on which a plurality of mono-cords can be deposited by direct metal deposition when they are worn.

As shown in the embodiment shown in FIG. 1, the one-piece bladed part can for example be an aeronautical turbojet compressor disc.

The invention can also be applied to any massive part whose edges are thin and wear out in operation, in particular movable sealing rings or even low-pressure turbine casings.

As shown in Figure 1, the thickness of the blade at its free end 12 is much smaller than its other dimensions. Due to this particularly thin thickness, for example less than 2 mm, it is possible to cover the free end 12 of a blade 11 by the direct deposition of metal from a plurality of mono-cords deposited on each other. . In other words, the thickness of the blade is entirely covered by the deposit of a single mono-cord.

To be representative of such a geometry, the cords of the plurality of cords of a characterization specimen can be arranged one above the other.

In addition, to faithfully represent the geometry of such a blade 11 of bladed one-piece part 10, the substrate used has a dimension, its thickness, equal to the thickness of the top of the blade of the bladed one-piece part 10 that it characterizes. The two other dimensions of the substrate are then chosen to be particularly large compared to this dimension.

For example, the thickness of the substrate can be at least 5 times, preferably at least 20 times, smaller than the other two dimensions of the substrate.

Figure 2 schematically represents a characterization specimen obtained by the method of the invention.

As described above, such a specimen 20 comprises a plurality of mono-cords 21 arranged on a substrate 22.

FIG. 3 represents a specimen 20 obtained in a process identical to that represented in FIG. 2 in a transverse view. In the embodiment shown, the test specimen 20 has a thickness e much less than its two other dimensions x and z.

As described above, the invention is not limited by the nature of the mono-cords or of the substrate. For example, the composition of the mono-cords may or may not be different from that of the substrate.

For example, the composition of the substrate / mono-cord pairs can be chosen from any pair of materials, provided that the two materials are weldable. For example, the composition of the substrate/mono-cord pairs can be chosen from among Ti17/Ti-6Al-4V, Ti-6Al-4V/Ti-6Al-4V, Inconel 718/Inconel 718, Inconel 718/Inconel 625, Inconel 625 /Inconel 718 or Inconel 625/Inconel 625.

In the embodiment shown in Figures 2 and 3, the specimen is obtained directly after the direct deposition of successive metals of the plurality of mono-cords.

In another embodiment represented in FIG. 4, the substrate is chosen with a width sufficient to obtain, after the deposition of the plurality of mono-beads 21, a part 23 in which several characterization specimens 20 can be machined, by example by cutting.

In such an embodiment, the method for manufacturing a characterization specimen 20 may further comprise, after the deposition of the plurality of single beads 21, a final step of machining the characterization specimens 20 in the part 23 obtained at the end of the step of direct deposition of metal on the surface of the substrate 22 described above.

Such an embodiment is particularly useful for producing test specimens 20 having a shape suitable for carrying out tensile tests.

As illustrated by Figures 2 to 4, it is possible to choose the substrate 22 to obtain with or a final machining step a characterization specimen 20 of the chosen shape.

Of course, such a machining step is carried out under conditions that do not affect the microstructure of the characterization specimen. Such a machining step can for example be carried out by water jet cutting.

As specified above, the dwell time can be determined by numerical evaluation of an equation linking the temperature at any point of the specimen to the dwell time.

In particular, when the specimen has a dimension much smaller than the other two, the temperature at any point (x,y) of the specimen can be expressed as a function of the time delay by the following equation:

[Math. 1] ,

with

[Math. 2] ,

where Q(t') is the power delivered by the laser during the deposition of a single bead, v the displacement speed of the laser, L the distance traveled by the laser, T0 the initial temperature, k the thermal conductivity of the substrate , c the specific heat capacity of the substrate, 1/2λ the thermal diffusivity of the substrate, h the convective coefficient between the air and the metal, ρ the density of the substrate and e the thickness of the substrate.

The numerical evaluation of the function described in equation [Math. 1] can be achieved, for example by means of the “integrate.quad” function of the “scipy” library of python.

The result of a numerical evaluation of this equation with the following parameters: k = 12 Wm ^-1 .K ^-1 , c = 630 J.kg ^-1 .K ^-1 , ρ = 4300 kg.m ^-3 , T0 = 20°C,
h = 30W.m ^-2 .K ^-1 , Q = 127.5 W corresponding to a substrate composed of Ti-Al6-V4 and a mono-cord composed of Ti-Al6-V4 is represented in FIG. 3 in the form of a graph showing the evolution of the temperature T as a function of the delay time t.

As also shown in FIG. 3, such a numerical evaluation makes it possible to determine the delay time t _tempo knowing the target temperature T _target .

In particular, such a method for determining the delay time is easily adaptable to any choice of substrate and/or single-bead since the equations [Math. 1] and [Math. 2] only depend on the geometry and parameters of the substrate and the single bead.

The proposed manufacturing process makes it possible to obtain a characterization specimen having a microstructure and a geometry identical to that of a bladed one-piece part. This process is also easily adaptable to any choice of substrate and/or mono-cord.

In addition, the manufacturing process is adaptable to obtain specimens with more complex geometries.

The use of a specimen obtained by the manufacturing process makes it possible to characterize, if necessary by means of destructive testing, a one-piece bladed part whose blades have been repaired by direct metal deposition. Such use can be used to characterize a new composition for the mono-bead, for example, and to determine the thermomechanical properties of the blade thus repaired.

Claims (10)

Method of manufacturing a characterization specimen (20) comprising direct deposition of metal in succession from a plurality of mono-cords (21) on a substrate (22), characterized in that, after the deposition of each mono-cord , a time delay is applied before depositing the next single bead, the delay time being defined so as to allow the deposited single bead to cool below a target temperature. Manufacturing process according to claim 1, in which the direct metal depositions are laser metal depositions. Manufacturing process according to claim 1 or 2, in which the mono-cords (21) of the plurality of mono-cords are composed of Ti-6Al-4V, inconel 625, inconel 718 or alternatively Hastelloy ® or Waspaloy ®. Manufacturing method according to any one of claims 1 to 3, in which the substrate (22) is composed of an alloy Ti17, Ti-6Al-4V, inconel 625, inconel 718, hastelloy ® or Waspaloy®. Manufacturing process according to any one of Claims 1 to 4, in which the target temperature is defined as the temperature reached after direct deposition of metal on the surface of a one-piece bladed part. Manufacturing process according to any one of Claims 1 to 5, in which the dwell time is determined by the numerical evaluation of an equation giving the temperature at any point of the specimen (20) as a function of the duration of delay. Manufacturing process according to any one of claims 1 to 6, in which the mono-cords (21) of the plurality of mono-cords are arranged one above the other. Manufacturing method according to any one of claims 1 to 7, further comprising a final machining step. Manufacturing process according to Claim 1 to 8, in which the substrate/deposition interface is in the useful zone of the specimen. Use of a characterization specimen (20) obtained by a method according to any one of claims 1 to 9 to characterize a blade (11) of a one-piece blisk (10) whose upper end (12) has been repaired by direct metal deposition.